48 AN ACCOUNT OF BRITISH FLIES. 
genus Aristolochia being cultivated in England, and one, A. clematis, 
which is a European species, has been found occasionally wild, 
but is not an indigenous form. Few plants outside the Orchidacee 
have become so modified for fertilization by insects as the one in 
question. The flowers are all brownish-green, contrary to what we 
should expect, as we are told in Darwin’s “‘ Origin of Species” “ that 
flowers have been rendered conspicuous in contrast with the green 
leaves and in consequence at the same time beautiful, so that they 
may be easily observed by insects.” And likewise that “if insects 
had not been developed on the face of the earth, our plants would 
not have been decked with beautiful flowers.” 
In this Aristolochia we have a decidedly inconspicuous flower, not 
only visited by insects, but having assumed most curious adaptations 
to ensure fertilization. It is strange that this family, which calls in 
the aid of insects more than most plants, should not have developed 
a more conspicuously coloured blossom to attract them during the 
time it has been forming those complicated habits and structures 
~ relating to fertilization ! 
Each of these greenish blossoms commences with an expanded lip. 
This passes into a funnel or throat (A), which is lined by hairs, so 
placed that they allow the entrance of an insect, but not its exit. 
This long funnel opens into a flask-shaped enlargement (B), in which 
are placed the generative organs. ‘This cavity is also lined by hairs, 
especially at the base, around the anthers. The stigmas (9) are 
placed above the anthers (¢), and curve over them, the anthers 
being surrounded by the hairs of the flask. 
Fertilization takes place in the following way: The Cecidomyia 
enters the throat and passes down it, the hairs being placed so 
as to allow its free passage. As soon as it enters the flask it crawls 
about until its back, which is laden with pollen, comes in contact 
with the stigma, and thus fertilizes them ; upon this taking place 
they spring up and assume an erect position. At the same time 
the hairs of the flask collapse and the anthers dehisce. The insect 
then crawling down, gets the pollen upon its back. While all this has 
‘been taking place the hairs of the funnel have withered up, and the 
Cecid or other insect, laden with fresh pollen, flies away to another 
blossom to repeat its experiences. But this is not all; as soon as the 
insects are free from the fertilized flower, the lip of the corolla 
bends over the entrance to the blossom, and thus effectually stops 
another fly from entering on a useless mission. The whole pedicel 
assumes a bent appearance, while the unfertilized ones are erect. 
This is, perhaps, one of the most curious adaptations that a plant 
